There are myriad types of cleaning compositions for cleaning textile fibers such as carpets, upholstery, drapery, clothing, bedding, linens, and the like. Most of these are based on soaps or other detergents which are generically referred to as "surfactants." By "surfactant" is meant a synthetic amphipathic molecule having a large non-polar hydrocarbon end that is oil-soluble and a polar end that is water soluble. Soap is also an amphipathic molecule made up of an alkali salt, or mixture of salts, of long-chain fatty acids wherein the acid end is polar or hydrophilic and the fatty acid chain is non-polar or hydrophobic. Surfactants are further classified as nonionic, anionic or cationic. Anionic or nonionic detergents are the most common.
Surfactants and soaps are formulated to loosen and disperse soil from textile fibers either physically or by chemical reaction. The soil can then be solubilized or suspended in such a manner that it can be removed from the fibers being cleaned. These function because the hydrophobic ends of the molecules coat or adhere to the surface of soils and oils and the water soluble hydrophilic (polar) ends are soluble in water and help to solubilize or disperse the soils and oils in an aqueous environment. A major problem associated with the use of surfactants in cleaning fibers has been that large amounts of water were generally required to remove the surfactants and suspended or dissolved particles. Also, surfactants generally leave an oily hydrophobic coating of the fiber surface. The inherent oily nature of the hydrophobic end of the surfactants causes premature resoiling of the fiber surface even when the surfaces have a surfactant coating which is only a molecule thick. The greater the concentration of surfactants used, the greater the potential for resoiling after cleaning. The residues left by surfactants also sometimes cause irritation or allergic reactions to people who are sensitive to these chemicals.
There are also environmental problems associated with the use of soaps and other surfactants. In addition to requiring relatively large amounts of water, some are non-biodegradable and some contain excessive amounts of phosphates which are also environmentally undesirable. It would therefore be desirable to utilize a composition in which the concentration of surfactants are kept at a minimum, while retaining the cleaning ability of the composition.
This concern over health and the environment has prompted an emphasis on the use of less toxic, more natural cleaning components. The quest for carpet cleaning compositions that have a balance of cleanability and resoiling resistance, however, has sometimes resulted in compositions containing unnatural components that have a greater potential to cause allergenic reactions and other health and environmental problems. Normal soaps prepared from the base hydrolysis of naturally occurring fats and oils are not suitable for carpet cleaning because of the propensity of their residues to attract soils. In order to make these residues less soil attracting, detergents are synthetically modified.
Another long existing problem in carpet cleaning is oxidative yellowing or "brown out" as it is commonly called. The usual conditions that increase the potential for brown out are a higher pH cleaner and/or prolonged drying times. Ordinarily the higher the concentration of solids in the cleaning composition the greater the potential for this oxidative yellowing to produce a noticeable discoloration on the carpet. Thus, by having a high pH and requiring large quantities of water to flush out residue, soaps and other surfactants tend to increase the risk of brown out.
The combination of a silicate fabric softening agent, a neutralizing or "souring" agent such as citric acid, a disintegrating agent comprising citric acid, hydrogen, carbonate and a filler material which may be ammonium sulfate, zeolite A or urea has been described in connection with the laundering of fabrics. In U.S. Pat. No. 4,814,095, "After Wash Treatment Preparation Based On Layer Silicate" the use of these compounds is demonstrated for use as a fabric softener. However, as noted on col. 3, lines 21-25 of that patent, the crucial performance feature of the composition, i.e. the fabric-softening property, is distinguished by the presence of a suitable layer silicate. As the patent discusses, the silicate layer is deposited on the textile fibers. While this may be advantageous for softening fabrics, it is undesirable for cleaning carpets, upholstery and other fabrics which are not thoroughly rinsed due to the fact that the excessive silicate residue can be abrasive. In addition, the residue leaves the carpet, upholstery or other material more prone to resoiling than carpet or upholstery without the residue. Furthermore, the large amounts of water required to flush silicate particulates from the carpet or upholstery increases the textile's drying time and increases the risk of brown out.
A significant improvement in the art of cleaning textile fibers, and carpets and upholstery in particular, is taught in U.S. Pat. No. 4,219,333. This patent shows that, when detergent solutions are carbonated under a positive gauge pressure and applied to the fibers at ambient temperature, the solution rapidly penetrates the fibers and, through the effervescent action of the carbonation, quickly breaks up and lifts the suspended soil and oil particles to the surface of the fiber from which they can be removed by vacuuming or transfer to an adsorptive surface such as to a rotating pad. Moreover, because less soap or other surfactant needs to be applied to the fibers, less water is needed to affect the cleaning, the fibers dry more rapidly than do fibers treated with conventional steam cleaning or washing applications, and little residue is left on the fibers. This results in less resoiling due to the reduced residue and in a decreased likelihood of brown out because of the more rapid drying of the fibers.
The invention claimed in U.S. Pat. No. 5,244,468 provides some resolution to the surfactant problem in that it claims the use of carbonated urea containing non-detergent compositions formed from the reaction between a carbonate salt and a naturally occurring acid or acid forming material. However, the invention still requires the presence of a positive gauge pressure to retain the proper degree of carbonation.
In the past, in order to prepare a carbonated solution it was necessary to pressurize the cleaning solution in a container with carbon dioxide from an outside source, e.g. a CO.sub.2 cylinder, and shake the container, preferably during CO.sub.2 introduction, to insure that the solution was carbonated. Carbon dioxide tanks necessary to accomplish this pressurization are heavy and inconvenient to have on site for attachment to sprayers when cleaning solution is being applied to carpets. The benefits of carbon dioxide as a volatile builder salt have outweighed the inconvenience of having a carbon dioxide tank on location during cleaning. In addition, a disadvantage of externally carbonating a solution under positive pressure is that excess carbon dioxide may be expelled into the air or surrounding atmosphere, and there is always the danger that carbon dioxide can be expelled accidentally from the pressurized cylinder in which it is contained.
It has also been known for a significant amount of time that hot cleaning solutions will clean textiles and other materials better than cool solutions. Many currently available carpets require an elevated temperature for proper cleaning. However, until the present invention, it has been unclear how to achieve the cleaning advantages of a carbonated solution combined with those of a heated solution. When a carbonated solution is heated, the cleaning efficiency gained by heating the solution is offset by the diminished solubility of the carbon dioxide in the solution. Thus, the more the solution is heated, the less carbonation it will carry for cleaning.
Additionally, it has also been known that the pH of a cleaning solution may significantly affect its cleaning efficiency. As was discussed above, new generation carpets are sensitive to elevated pH solutions, and will be damaged if an alkaline solution stays on the carpet for any significant length of time. Until the present invention, it has been difficult to obtain the benefits of elevated pH solutions without affecting the stain resistance of new generation carpets, or causing brown out.
Thus, there is a need for a cleaning solution which combines the benefits of a carbonated solution and those of a heated solution, without the traditional problems associated with surfactants, and other fillers.